Spline for rotary actuator

ABSTRACT

An improved spline for drivingly connecting the armature of a rotary solenoid actuator to an output shaft driven by the armature comprises needle bearings lodged between confronting flutes of the armature and the driven shaft. The flutes have flat angularly disposed longitudinal walls so as to make line contact with the needle bearings.

United States Patent [1 1 Yost July 3, 1973 [54] SPLINE FOR ROTARYACTUATOR 3,136,930 6/1964 Straub 335/228 3,320,822 5/1967 Tatom 335/228X [75] Inventor: Dam", Ohm 3,308,410 3/1967 Biser 335/223 73 A L d I Daton,Oho sslgnee e ex nc y 1 Primary Examiner-George Harris [22] Fil d; St, 5, 1972 Attorney-H. Talman Dybvig An improved spline for drivinglyconnecting the arma- [52] US. Cl. 335/228, 74/89 ture of a rotarysolenoid actuator to an output shaft [51] Int. Cl. H0 7/08 d i en by thearmature comprises needle bearings [58] Field Of Search 335/228, 272;lodged between confronting flutes of the armature and 3 39 the drivenshaft. The flutes have flat angularly disposed longitudinal walls so asto make line contact with the [56] References Cited needle bearings.

UNITED STATES PATENTS 11/1960 Leland et al 74/88 9 Claims, 5 DrawingFigures Bum July 3, 1913 3,743,987

JlE-I 1 SPLINE FOR ROTARY ACTUATOR BACKGROUND OF THE INVENTION 1. Fieldof the Invention This application relates to rotary solenoid actuatorsof the type in which an armature is drawn helically toward anelectromagnet and, more particularly, to a spline connection between thearmature and a shaft driven thereby, the spline connection representinga helical to purely rotary motion converter enabling a driven shaft toderive rotary torque from the armature while not moving axially with thearmature.

2. Description of the Prior Art Prior art examples of solenoid deviceswhich enable a helically advancing armature to transmit only itsrotational movement to the driven shaft appear in United States Pat.Nos. 2,959,969, 3,320,822 and 3,308,410.

SUMMARY OF THE INVENTION Helical to rotary motion converters known inthe prior art have been found wanting in compactness and designsimplicity. With the present invention the desired compactness andsimplicity is obtained by providing a bore through the solenoid armaturein which the driven shaft is received, providing confronting flutes inthe interior wall in the bore through the armature and the exterior wallof the shaft, and keying or splining the shaft to the armature by meansof elongated needle bearings which allow the armature to move axially onthe shaft with a minimum of friction.

DESCRIPTION OF THE DRAWING In the drawing FIG. I is a perspective viewof a rotary solenoid actuator embodying the present invention.

FIG. 2 is a side elevation view of the actuator.

FIG. 3 is a fragmentary section view taken substantially along the line3-3 of FIG. 1.

FIG. 4 is a section view taken substantially along the line 4-4 of FIG.2.

FIG. 5 is an enlarged, partly fragmented section view taken along theline 5-5 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The rotary solenoid actuatorillustrated in the drawing comprises an electromagnet assembly housed ina generally cylindrical ferromagnetic casing 10. As best appears in FIG.5 the electromagnet assembly comprises a ferromagnetic base plate 12press fitted into the casing and having an integral upstanding generallycylindrical core member 14. The core member 14 is smaller in diameterthan the interior of the casing 10 and the annular space between thecasing 10 and the core member 14 is occupied by a solenoid coil 16having terminal connections 17a and 17b which pass through suitableapertures in the casing 10.

Fitted within a central aperture through the core member 14 is a sleevebearing 30 journalling a shaft 28. Encircling the shaft 28 is aferromagnetic armature 18, the armature being attracted to the coremember 14 upon energization of the coil 16.

The armature 18 has a cylindrical head 19 which is of a reduced diametersized to enter an annular plate 20. The head 19 is peened as shown at 21to fixedly lock the plate to the armature 18. The surface of the plate20 which confronts the casing 10 has three inclined arcuate recesses 22stamped into the face thereof. The stamping of the recesses into oneface of the plate 20 produces buldges 22a in the opposite face of theplate 20. It can be noted that the recesses 22 are spaced equally aboutthe axis of the shaft 28.

Similarly disposed recesses 25 are stamped into an annular flange 26integral with and directed inwardly from the casing 10. As shown in FIG.3, the recesses in the flange 26 are oppositely inclined with respect tothe recesses in the plate 20 so that one recess has its deepest end at aclockwise extreme and the other recess has its deepest end at acounterclockwise extreme. Ball elements 24 are interposed between therecesses 22 and 25, there being one ball element between each pair ofconfronting recesses.

The arrangement of the ball elements 24 and the recesses 22 and 25 issuch that when the plate 20 is rotated in the clockwise direction asviewed in FIG. I the ball elements 24 roll to the shallow ends of theconfronting recesses, and the separation between the armature 18 and thecore member 14 approaches a maximum separation. When the plate 20 isrotated oppositely in a counterclockwise direction, the ball elements 24roll to the deep ends of their respective recesses and the armature 18makes its closest approach to the core member 14.

The shaft 28 is given a clockwise bias as it appears in FIG. 1 by meansof a return spring 46 caged within a circular array of lugs 48 struckoutwardly from a caging plate 51 affixed to base plate 12 by anysuitable means such as spot welding. The return spring 46 is a spiralspring having its innermost end seated in a suitably located slot, notshown, in the shaft 28 and having a tongue 47 struck outwardly from itsoutermost convolution for booking engagement to any one of the lugs 48.By proper selection of the lug 48 engaged by the tongue 47 a biasnormally sufficient to hold the ball elements 24 in the shallow ends ofthe recesses 22 and 25 can be preselected.

As best appears in FIG. 5 the armature 18 is received within the centerof the annular flange 26 with a slight clearance. Upon energization ofthe coil 16 a flux path exists through the core piece 14, across itsbase plate 12 upwardly through the casing 10, across the flange 26, thenacross the relatively small clearance separating the flange 26 from thearmature 18. The armature l8 seeks to close this flux path by movingaxially toward the core piece 14.

It can thus be seen that upon energization of the coil 16 the armature18 will be attracted toward the pole piece 14 so that the ball elements24 are compressed between the recesses 22 and 25 and thereby inducedroll to the deeper ends of such recesses. The armature is thus inducedto rotate helically toward the pole piece 14 and against the bias of thespring 46. The ball elements acting in the recesses 22 and 25 can besaid, accordingly, to comprise an axial to helical motion conversionmeans. The primary purpose of the present invention is to so couple thearmature 18 to the shaft 28 that only the rotary component of thishelical motion is transmitted to the shaft 28.

As appears in FIG. 5 the shaft 28 has a diametrically enlarged collarportion 32 which is larger than the diameter of the shaft, either at itsuppermost or lowermost end, and especially regions adjacent thereto.Flutes or indentations 38 which are V-shaped in cross section are milledor broached longitudinally along the length of the collar portion 32,there being four such flutes at equiangular intervals around the axis ofthe shaft 28. The enlargement of the collar portion 32 compared to thediameter of the shaft 28 at other portions along its length is toaccomodate and thereby simplify the milling of the flutes 38.

As best appears in FIG. 4 the armature 18 has an aperture 34 sized toloosely receive the collar portion 32. Four equiangularly spacedV-shaped flutes or indentations 36 are milled or broached into theinterior wall of the armature and throughout the axial length of thearmature. Needle bearings 4th, which are preferrably a hardened steel,are sized to enter between confronting flutes 36 and 38 in such fashionthat when four needle bearings 40 are inserted, each individuallybetween confronting pairs of flutes 36 and 38 in the manner shown inFIG. 4, the armature 1% is aligned coaxially with the shaft 28. Thebearings 40 have a circumferential interflt with the flutes 36 and 38which prevents relative rotation between the armature and the shaft, butare not axially confined by the flutes.

Those skilled in the art will recognize that the circumferentialinterfit can be achieved with only two diametrically disposed needlebearings or could be achieved with three or more needle bearingsdisposed at equiangulai positions. However, since it is normally aneasier matter to mill or broach diametrically opposite sides of a workpiece, and since the tolerance to which the flutes 36 and 38 must beformed can be reduced by increasing the number of flutes, the preferredembodiment employs four needle bearings 40 and accomodating flutes asshown in FIG. 4. The needle bearings are retained axially adjacent thearmature 18 by means of an annular spacer 42 surrounding the shaft 28 inthe air gap between the armature and the core piece 14 and a cooperatingannular spacer 44 located above the armature 18. The spacer 44 isconfined by a split spring ring 54 seated in an annular groove 55located in the collar portion 32 of the shaft 28.

in the preferred practice of this invention the axial length of theneedle bearings 4th is only slightly less than the axial space availablebetween the spacers 42 and 44. This assures that the armature 18 willreceive substantially full bearing support from the needle bearings 4th,not only in its uppermost position as shown in FIG. but also in itslowermost position after the armature 18 has advanced downwardly towardthe pole piece K4. With such construction the primary sliding motionoccurring during operation of the solenoid is a sliding motion of thearmature 18 on the needle bearings M which remain relatively stationary.Since the needle bearings make only line contact with the side walls ofthe flutes 36 in the armature, sliding friction is nominal and thelikelihood of seizure between any of the bearings and its confiningflutes 36 is virtually nonexistant.

Axial travel of the shaft 28 is relative to the core piece M isprecluded by the spacer 42, which abuts the shoulder portion 52 in theair gap region, acting in cooperation with a spacer 50 encircling theshaft 28 adjacent the return spring 46. The bottom end of the shaft 28is swaged to form a shoulder 52 on the shaft 28 which retains the spacer50.

it can be noted in FIG. 5 that the length of the shaft 28 between thecollar portion 32 and the shoulder 52 is occupied entirely by the spacer42, the core piece 114 and its integral base plate 12, the return spring46 and its adjacent spacer 50. The return spring 46 is therefore a partof the structure which supports the shaft 28 against axial movementrelative to the core piece 114. The security with which the shaft 28 issupported against axial movement is thus dependent upon the ability ofthe spring 46 to resist collapse in the event the shaft 28 is subjectedto axial loading. While the axial loading on the shaft 28 may at firstappear nominal because the needle bearings W allow the armature 18 toslide axially on the shaft 28, the axial loads to which the shaft issubjected cannot be entirely ignored. it is true, of course, that whenthe coil 16 is energized to move the armature l8 downwardly as itappears in FIG. 5,

' and axial loading on the shaft 28 will be small because the armaturel8 slides freely on the needle bearings 40. However, when the coil 16has been deenergized and the spring 46 operates to return the armatureby an opposite rotation of the armature 118, the armature 18 isaccelerated upwardly as it appears in FIG. 5 and the resultant upwardmomentum of the armature must be absorbed in part by an impact with thesplit ring 54. The force of this impact must be ultimately absorbed byan impact of the spacer 50 against the return spring 46. it is found,however, that the upward momentum generated in the armature lb duringthe return stroke is not great enough to adversely effect the veryspring which generated the momentum.

in some applications for the rotary solenoid it is required that theshaft 28 have an extension, not shown, passing centrally through thereturn spring 46 for engagement with a load device located below thespring 46. in such cases it is found desirable that a second splitspring ring, not shown, be engaged to a suitably located annular groove,not shown, in the shaft 28, the second split ring being located betweenthe return spring 46 and the base plate 12. When the second split ringis employed, it cooperates with the spacer 42 to secure the shaft 28against axial motion relative to the core piece 14, thus allowingelimination of the spacer 50 and the shoulder 52, and extension of theshaft 28 downwardly beyond the return spring 46.

Although a preferred embodiment of the invention has been described, itwill be understood that within the purview of this invention variouschanges may be made in the form, details, proportions, and thearrangement of parts without departing from the scope of the presentinvention as more particularly expressed in the following claims.

Having thus described my invention, 1 claim:

1. in a rotary actuator device comprising an electromagnet assemblyrotatably supporting a shaft, an armature having a bore receiving saidshaft and movable axially along said shaft in response to energizationof said electromagnet assembly, axial to helical motion conversion meanscoacting between said electromagnet assembly and said armature to rotatesaid armature helically along the axis of said shaft, and helical torotary motion conversion means coacting between said armature and saidshaft to rotate, without axially moving, said shaft, the improvementwherein said helical to rotary motion conversion means comprises aplurality of first indentations in said shaft circumferentially spacedabout the axis of said shaft, an equal number of second indentations inthe interior wall of said bore, each of said first indentationsconfronting a second indentation, a plurality of bearing members, therebeing a one piece bearing member circumferentially interfitting eachfirst indentation and its confronting second indentation, one of thefirst and second indentations interfitted by each bearing member beingan axially extending flute to allow relative axial movement of itsinterfitting bearing member, and means coacting between saidelectromagnet assembly and said shaft to support said shaft againstaxial motion relative to said electromagnet assembly.

2. The rotary actuator device of claim 1 in which the other of the firstand second indentations interfitted by each bearing member is also anaxially extending flute and said bearing members are needle bearings.

3. The rotary actuator device of claim 2 in which said bore has agenerally cylindrical wall and said second indentations are flutes insaid wall extending axially throughout the length of said wall.

4. The rotary actuator device of claim 2 in which said flutes areV-shaped in cross section and have line contact with said needlebearings.

5. The rotary actuator device of claim 1 in which said equal number isfour.

6. The rotary actuator device of claim 1 in which said shaft has anaxially extending collar portion larger in diameter than portions ofsaid shaft adjacent thereto,

and in which said first indentations are flutes axially traversing saidcollar portion.

7. A spline assembly to nonrotatably couple a shaft with a membermovable axially along said shaft, said member having a boretherethrough, said shaft having a radially enlarged collar portionreceived in said bore, said collar portion having diametrically disposedaxially extending flutes traversing the axial length thereof, said borehaving diametrically disposed axially extending flutes traversing thelength thereof, the flutes of said collar portion confronting the flutesof said bore, and elongated needle bearings interposed between saidconfronting flutes and circumferentially interfitting said flutes.

8. The spline assembly of claim 7 in which the diametrically disposedflutes in each of said collar portion and said bore comprise two pairs,said flutes in each of said collar portion and said bore disposed atequiangular positions about the axis of said shaft.

9. The spline assembly of claim 7 in which said flutes each have aV-shaped cross section in planes perpendicular to the axis of saidshaft.

1. In a rotary actuator device comprising an electromagnet assemblyrotatably supporting a shaft, an armature having a bore receiving saidshaft and movable axially along said shaft in response to energizationof said electromagnet assembly, axial to helical motion conversion meanscoacting between said electromagnet assembly and said armature to rotatesaid armature helically along the axis of said shaft, and helical torotary motion conversion means coacting between said armature and saidshaft to rotate, without axially moving, said shaft, the improvementwherein said helical to rotary motion conversion means comprises aplurality of first indentations in said shaft circumferentially spacedabout the axis of said shaft, an equal number of second indentations inthe interior wall of said bore, each of said first indentationsconfronting a second indentation, a plurality of bearing members, therebeing a one piece bearing member circumferentially interfitting eachfirst indentation and its confronting second indentation, one of thefirst and second indentations interfitted by each bearing member beingan axially extending flute to allow relative axial movement of itsinterfitting bearing member, and means coacting between saidelectromagnet assembly and said shaft to support said shaft againstaxial motion relative to said electromagnet assembly.
 2. The rotaryactuator device of claim 1 in which the other of the first and secondindentations interfitted by each bearing member is also an axiallyextending flute and said bearing members are needle bearings.
 3. Therotary actuator device of claim 2 in which said bore has a generallycylindrical wall and said second indentations are flutes in said wallextending axially throughout the length of said wall.
 4. The rotaryactuator device of claim 2 in which said flutes are V-shaped in crosssection and have line contact with said needle bearings.
 5. The rotaryactuator device of claim 1 in which said equal number is four.
 6. Therotary actuator device of claim 1 in which said shaft has an axiallyextending collar portion larger in diameter than portions of said shaftadjacent thereto, and in which said first indentations are flutesaxially traversing said collar portion.
 7. A spline assembly tononrotatably couple a shaft with a member movable axially along saidshaft, said member having a bore therethrough, said shaft having aradially enlarged collar portion received in said bore, said collarportion having diametrically disposed aXially extending flutestraversing the axial length thereof, said bore having diametricallydisposed axially extending flutes traversing the length thereof, theflutes of said collar portion confronting the flutes of said bore, andelongated needle bearings interposed between said confronting flutes andcircumferentially interfitting said flutes.
 8. The spline assembly ofclaim 7 in which the diametrically disposed flutes in each of saidcollar portion and said bore comprise two pairs, said flutes in each ofsaid collar portion and said bore disposed at equiangular positionsabout the axis of said shaft.
 9. The spline assembly of claim 7 in whichsaid flutes each have a V-shaped cross section in planes perpendicularto the axis of said shaft.